LOW EMISSIVITY PAINT

Abstract: Paints with a low emissivity in the infrared region are useful for marking objects to stand out when viewed in infrared sensitive viewing devices such as thermal imaging equipment, and for camouflaging vehicles and equipment. Such paints can be applied to objects by firing paints in a capsule from a projectile firing mechanism. One such paint can be formulated by providing chlorinated polymer, plasticizing resin, one or more pigments and clay thickener, all between 1 % and 10 % by weight and energy reflective particles between 10 % and 60 % together with a small amount of dye and possibly of solvent. The energy reflective particles may be aluminium or silver plated copper flake, for example.

Description: LOW EMBSIVΠΎ PAINT The invention relates to a paint, particularly a low emissivity paint, that is a paint which provides a low emissivity of incident electromagnetic energy. In the past, vehicles and installations have been camouflaged in a variety of different ways, all of which have the effect of making the subject blend-in visually with its background. For this purpose, paints have been employed with a colour and finish to match the surroundings, such as matt blues and greys for naval theatres, and matt browns and greens for terrestrial theatres. With the advent of electronic imaging systems which utilise emitted electromagnetic radiation, it has become necessary to camouflage equipment not only visually, but also to camouflage electronically, by reducing the amount of radiation emitted that such devices can detect. One type of device, known as a Thermal Observation Gunnery Sight, detects emitted infrared radiation in the far red wave bands of 3 to 5 and 8 to 14 microns using thermal imaging apparatus, and in order to camouflage equipment from detection, it is necessary to reduce infrared emissions to a level where the camouflaged object has a similar emissivity to its background. For example, vegetation typically has an emissivity of about 0.5-0.6. Typically, materials which have a shiny or lustrous finish, such as metals, have a low emissivity, a typical metallic lacquer having an emissivity of about 0.5. Paints with metallic constituents are widely known in for example, the automotive industry; however these do not provide good visual camouflage and also do not have a low emissivity because the pigments used disrupt the action of the metallic particles. Conversely, materials with matt finishes provide good visual camouflage, but have a high emissivity. It is an object of the present invention to mitigate problems such as this. According to the invention there is provided a paint comprising a binder, a pigment, a thixotropic agent and electromagnetic energy reflective particles, wherein the particle size of the pigment is adapted to facilitate a reduction in the emissivity of the paint of electromagnetic energy of far infrared wavelengths. As used herein, the term far infrared wavelengths means from 0.9 to 100 microns. It is preferred that the pigment comprises from 55 to 100% of pigment particles in the size range from 0.01 to 0.095 microns, more preferably in the range from 0.025 to 0.075 microns. It is most preferred that the pigment comprises from 75 to 100% of - gment particles of about 0.05 microns. Thus, it has surprisingly been found that a paint which has a matt finish and includes pigments whilst retaining a relatively low emissivity of electromagnetic radiation can be obtained by adapting the pigment particles to prevent them interfering with the emissivity reducing properties conferred on the paint by the energy reflective particles. A low emissivity in this context means emissivities from 0.1 to 0.6. The energy reflective panicles preferably comprise silver plated copper flake, which has the advantage of being relatively inexpensive. Aluminium and other reflective panicles, such as metal-plated microspheres and metal plated fibres are also suitable. Water can be added to provide the consistency required for proper application, or a solvent can be substituted, comprising between 10% and 60%. The paint may comprise a plasticising resin to give flexibility to the formulation, especially when a non-flexible binder is used. It may also be provided with a small amount of dye to enhance or modify colour. Suitable binders include solvent-soluble polymers, and a particularly suitable binder is a chlorinated polymer, due to its durability and fire-retardant properties. Suitable pigments include cadmium sulphide P101 , iron blue 510D and red oxide 470, particularly as the visible appearance of the paint will be of importance because the paint may have to blend in with ordinary paints and still provide low emissivity in the infrared region. In another aspect of the invention there is provided a paint with low emissivity in the far infrared region as hereinabove described, packed in a capsule suitable for firing from a projectile-firing device. Typically, commercially available pigments have a particle size of from 0.5 to 1.5 microns, and in order to prepare paints embodying the invention it is usually necessary to first reduce the particle size by grinding with any suitable machine to reduce the particle size to the desired range. Once this has been accomplished the paint may be formulated and mixed using known techniques to produce the desired colour and consistency. A variety of different binders may be used depending on the precise properties which are required in the paint. Examples of suitable binders are non-reactive polyurethane resins, moisture-cured polyurethane resins, acrylic-urethane resins and acrylic resins. Suitable thixotropic agents include modified clays, hydrogenated castor oil derivatives, fumed silica, and fibrous polyolefins. The thixotropic agent serves not only to provide a desired consistency, but also acts to keep the energy reflecting particles dispersed and in suspension in the paint. Where a solvent is required, examples of suitable solvents include aromatic hydrocarbons, aliphatic esters, aliphatic ketones and glycol esters. An example of a typical formulation of paint embodying the invention comprises: - Chlorinated Polymer 1 - 10% Plasticizing Resin 1 - 10% Pigment, each 1 - 10% Cadmium Sulphide P101 , Iron Blue 510D, Red Oxide 470 Dye less than 1% Clay Thickener 1 - 10% Silver Plated Copper Flake 10 - 60% Solvent 10 - 60% As will be appreciated the solvent constituent is optional, and the paint may be pigmented in all standard colours. A paint with this formulation is inherently stable and so can be packaged very simply. For example, the material can be supplied in capsules for delivery by missiles projected by firearms or mortars, for example. Being very light, the capsules do not affect the flight of the missiles and so a very accurate flight path can be predicted and the paint will serve as an effective target marker. The marked target can then be viewed by an infrared viewing device and action taken as appropriate on the now easily-located target. Other examples of packaging include aerosol containers, other spray cans or a tin of conventional brush application paint. Paints embodying the invention can also be used to "invisibly" mark vehicles and apparatus, so that the markings can only be seen by personnel using thermal imaging equipment. Thus, although the paint may appear in visible light as a normal paint, when a painted area is viewed on an article in infrared light, the area will appear in sharp contrast to the adjacent non-painted area because the level of emissivity is reduced by the paint. A typical level of emissivity would be 0.6 or below.

Claims: CLAIMS 1. A paint comprising a binder, a pigment, a thixotropic agent and electromagnetic energy reflective particles, wherein the particle size of the pigment is adapted to facilitate a reduction in the emissivity of the paint of electromagnetic energy of far infrared wavelengths. 2. A paint according to claim 1 , wherein the pigment comprises from 55 to 100% of pigment particles in the size range from 0.01 to 0.095 microns. 3. A paint according to claim 1 , wherein the pigment comprises from 55 to 100% of pigment particles in the size range of 0.025 to 0.075 microns. 4. A paint according to claim 1. wherein the pigment comprises from 75 to 100% of pigment particles of about 0.05 microns. 5. A paint according to any preceding claim, wherein the energy reflective particles comprise silver plated copper flake. 6. A paint according to any of claims 1 to 4, wherein the energy reflective particles comprise aluminium. 7. A paint according to any preceding claim, comprising a solvent of at least 10% by weight of the paint. 8. A paint according to any preceding claim, including water. 9. A paint according to any preceding claim, wherein the thixotropic agent includes modified clays, and/or hydrogenated castor oil derivatives, and/or fumed silica, and/or fibrous polyolefins. 10. A projectile for firing from a gun comprising a container of paint as defined in any of claims 1 to 8. 11. An aerosol spray comprising a container of paint as defined in any of claims 1 to 8.

Inventors: TUSCH KLAUS NORBERT, TUSCH, KLAUS, NORBERT
Applicants: COLEBRAND LTD, TUSCH KLAUS NORBERT, COLEBRAND LIMITED, TUSCH, KLAUS, NORBERT
Application year: 1994
Main classification: C09D5
IPC codes: C09D5, F41H3